MT. PLEASANT, TN, USA
N174OD
BEECH A36
WHILE CRUISING THE ENGINE DEVELOPED A VIBRATION AND STARTED RUNNING ROUGHLY. THE PILOT REDUCED POWER AND ESTABLISHED A TRACK FOR AN EMERGENCY LANDING TO A NEARBY COUNTY AIRPORT; THE AIRPLANE CRASHED ABOUT ONE MILE SHORT OF THE AIRPORT. EXAMINATION OF THE ENGINE ASSEMBLY DISCLOSED THAT A PIECE OF THE CRANKCASE WAS BROKEN ABOVE NUMBER 2 CYLINDER AND THE CYLINDER WAS PARTIALLY SECURED BY ONE HOLD DOWN NUT ON THE BOTTOM LEFT SIDE. FURTHER EXAMINATION REVEALED FRETTING BETWEEN THE CYLINDER FLANGE AND THE ENGINE CASE. ALL CRANKCASE FRACTURES SHOWED SIGNS OF OVERLOAD FAILURE. THE ENGINE MAINTENANCE LOGS DISCLOSED THAT THE ENGINE'S CRANKCASE HAD BEEN REPLACED ON 10/24/90; THIS ENGINE MALFUNCTION OCCURRED 258 HOURS LATER. SUBSEQUENT TO THIS ACCIDENT, CONTINENTAL MOTORS ISSUED A SERVICE BULLETIN WHICH INCREASED THE TORQUE VALUE FOR THE CYLINDER HOLD DOWN NUTS, AND INSTRUCTED THAT THE STANDARD SIX POINT HOLD DOWN NUTS BE REPLACED WITH TWELVE POINT NUTS DURING OVERHAUL.
THE MANUFACTURER'S FAILURE TO PROVIDE ADEQUATE TORQUE INFORMATION WHICH RESULTED IN THE LOSS OF TORQUE ON THE CYLINDER HOLD DOWN NUTS AND THE COMPLETE LOSS OF ENGINE POWER.
Source: NTSB Aviation Accident Database
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